有的button不能添加点击事件？

[lyuxxx]

UIButton *btn1 = [UIButton buttonWithType: UIButtonTypeCustom];
    [btn1 setImage: [UIImage imageNamed: @"cart"] forState: UIControlStateNormal];
	[btn1 addTarget:self action:@selector(log) forControlEvents:UIControlEventTouchUpInside];

    UIButton *btn2 = [UIButton buttonWithType: UIButtonTypeCustom];
    [btn2 setImage: [UIImage imageNamed: @"setting"] forState: UIControlStateNormal];
	[btn2 addTarget:self action:@selector(log) forControlEvents:UIControlEventTouchUpInside];

    UIButton *btn3 = [UIButton buttonWithType: UIButtonTypeCustom];
    [btn3 setImage: [UIImage imageNamed: @"user"] forState: UIControlStateNormal];
	[btn3 addTarget:self action:@selector(log) forControlEvents:UIControlEventTouchUpInside];

demo里面的代码添加，只有btn1会响应事件

[Desgard]

测试了，确实是这样。好奇葩的问题。。我看看原因是什么。感谢iss！